Master Gardener: Grafted tomato plants put to the test

Ideally, grafting can extend the growing season for tomatoes in Arizona. Photo by Carol Howerton

By Carol Howerton

Carol Howerton. Submitted photo

Grafted tomato plants are all the rage these days. They promise increased disease resistance and hardier, more vigorous plants with bigger and better yields. Sounds great, right? But these plants are pricey, ranging from $8-$20 per plant. Are they worth the extra cost for the home gardener in our desert environment?

For the past three years, the Master Gardeners at the Maricopa Agricultural Center have been grafting and growing tomatoes to find the answer to this question. We chose heirloom varieties that everyone loves, like Brandywine and Cherokee Purple because they are not known to do well in our hot climate. Could we find a way through grafting to extend the growing season and harvest more of these wonderful tomatoes? And could we develop a system that would be effective and low-cost so anyone can graft tomatoes at home?

The rootstock varieties chosen were drought-tolerant and vigorous, but any hardy tomato variety can be used such as the Super Sweet 100 Cherry or Sweet Million. Once the desired tomato variety (called the scion) was grafted on to the rootstock, they were put into a healing chamber for 7-10 days.

The chamber can be any enclosure that blocks or limits light and allows for humid conditions. We used Styrofoam ice chests, but plastic storage bins covered with towels also work well. The ideal temperature inside the healing chamber is 80-85 degrees and, to keep the humidity in the 90-95 percent range, we misted the plants daily using spray bottles.

The goal of the healing chamber is to create a low-stress environment where the scion and rootstock can fuse and grow together as one plant. No light is let in for the first two days. Gradually light is increased to bring the plants back to normal growing conditions.

Many of the grafted plants do not survive for a variety of reasons. Genetic incompatibilities, mismatched stem size of the rootstock and scion or the healing environment itself are a few of the reasons for graft failures. No one will have a 100 percent success rate.

When transplanting a grafted plant into your garden, be sure to have the graft union above the soil line or the rootstock can regrow and take over your garden. You will see the graft line as a scar at the graft point.

Grafting is exciting and fun, not difficult and, with the right supplies, pretty inexpensive to do at home. The problems here in Maricopa and Pinal County are more about disease spread by insects than soil-borne diseases and our hot dry climate. We planted grafted and non-grafted varieties in our Demonstration Garden and in home test gardens. To answer our question of whether it is worth doing yourself or paying higher prices for grafted plants, I will leave that up to you to decide. We did not see any noticeable increase in production or increase in the growing season.